优化ImageView，在使用ListView或GridView的时候，每次更新图片的时候，在显示新的图片和旧的图片一样大小的时候，不需要去重新计算大小

本文介绍了一个名为OptimisedImageView的自定义视图组件，该组件通过智能处理图片尺寸变化来避免不必要的布局请求，从而提高Android应用中ImageView的性能表现。

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import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Build.VERSION;
import android.os.Build.VERSION_CODES;
import android.util.AttributeSet;
import android.widget.ImageView;

public class OptimisedImageView extends ImageView {

    private boolean mIgnoreNextRequestLayout = false;

    public OptimisedImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void setImageDrawable(final Drawable newDrawable) {
        if (VERSION.SDK_INT < VERSION_CODES.ICE_CREAM_SANDWICH) {

            // The currently set Drawable
            final Drawable oldDrawable = getDrawable();

            if (null != oldDrawable && oldDrawable != newDrawable) {
                final int oldWidth = oldDrawable.getIntrinsicWidth();
                final int oldHeight = oldDrawable.getIntrinsicHeight();

                /**
                 * Ignore the next requestLayout call if the new Drawable is the
                 * same size as the currently displayed one.
                 * */
                mIgnoreNextRequestLayout = oldHeight == newDrawable.getIntrinsicHeight()
                        && oldWidth == newDrawable.getIntrinsicWidth();
            }
        }

        // Finally, call up to super
        super.setImageDrawable(newDrawable);
    }

    @Override
    public void requestLayout() {
        if (!mIgnoreNextRequestLayout) {
            super.requestLayout();
        }

        // Reset Flag so that the requestLayout() will work again
        mIgnoreNextRequestLayout = false;
    }

}